1. Field of the Invention
The present invention relates to large conveyor belt systems which operate over inclines and declines, and the installation of the belts thereon, and, more particularly, to a method and apparatus for the installation of such belts by lowering them from elevated portions of such systems.
2. Background
Modern mining operations often employ conveyor belts to transport the mined materials from the excavation site to a remote plant for processing and/or loading. Given the scale of modern mining operations, such as the open pit techniques used for mining coal, copper and other ore, tar sands, and so forth, the proportions of these conveyor belt systems are often truly massive. To help illustrate this, FIG. 1 shows a perspective view of such a system, and how this may traverse great distances of open terrain. Individual conveyor runs are frequently several miles in length, and the belt may be several feet. Being that the belt must be able to handle the weight and impact of the mined materials, it must be very heavily constructed, typically of steel cables encased in a block or plies of rubber. For example, some belts may be better than 1.5 inches thick and some 10 feet wide, and so may weigh several hundred pounds for each yard of length. Thus, in a conveyor system which is several miles long, the weight of the belt alone may range in the thousands of tons.
Being that mining operations are frequently located in rugged terrain, the conveyor belt systems often must traverse very steep and lengthy inclines and declines. Given an elevation change of hundreds and sometimes thousands of feet, it becomes apparent that the loads which are generated by the weight of the massive runs of belt are tremendous in such a system. These loads become a very serious problem when it is necessary to install a new belt on a conveyor system, or it is necessary to repair or replace sections of an existing belt. Not only is the operation rendered exceedingly difficult and dangerous by these loads, but it can be economically disastrous for the operation of the conveyor system to be interrupted for any significant period of time while carrying out the work and setting up the heavy equipment which is required for handling these loads.
These techniques which have previously been employed to install belts on such conveyor systems have been marked by grave drawbacks and limitations. The usual approach has been to position a roll of the belt material at the bottom of the conveyor run, and then install some sort of attachment fitting on the end of the roll. The attachment fitting is then connected to a bulldozer or other vehicle so that this pulls the belt up the slope. However, the point has often been reached with modern conveyor systems where the belt is simply too heavy for any available vehicle to be able to do this. Furthermore, the slope is often much too great for the operation of a vehicle.
Attempts have been made to overcome these problems by using winches which are anchored into the earth. Typically, a series of cement foundations are poured for the winch, and the winch is moved up the slope as each roll of belt is put on the system. However, the weight of the belt necessitates the use of extremely large winches, and the process of moving these winches step-by-step up the mountain, and then anchoring and rigging them for each roll of belt, is prohibitively time-consuming and expensive. While some operators have tried to circumvent these problems by using a very large winch which has sufficient cable capacity that it can pull the belt all the way up the slope without being moved, the huge size of the drum and associated drive assembly necessary to do this renders this system excessively expensive and very difficult to transport to the top of the conveyor system, which may be located at some remote, elevated site; furthermore, when using a system of this type, the weight of the very long pull cable which is required to span the length of the run becomes a serious problem in itself.
In addition to being expensive and difficult to practice, the conventional approach of installing these belts by pulling them up the slopes, whether using a tractor or winch, is fraught with extreme danger. Since the belt is necessarily supported by the pulling device during this operation, in the event that the belt separates from the pulling device (e.g., the cable breaks or comes loose from the end of the belt), or the pulling device (e.g., the winch) becomes disengaged from its anchor, the resultant runaway belt will cause virtually certain massive destruction of equipment, as well as very possible loss of life. On a lesser scale, the fact that this technique requires the concentration of massive loads on the belt (at the attachment plate) means that this frequently results in serious damage to the structure of the belt, which may cause subsequent operational failure or at least necessitate expensive repairs.
Another serious difficulty which is encountered with these conventional installation techniques stems from the usual arrangement of the carrying and return idlers of the conveyor belt systems. As is shown in FIG. 1, the carrying idlers 12 and return idlers 14 are typically installed in a series of support structures or platforms 16. The carrying idlers 12 are frequently arranged in the form of a trough so as to shape the belt into an appropriate configuration for carrying the ore or other material, and the return idlers 14 are mounted beneath these on the underside of the support platforms 16. There is thus very little space above the return rollers 14 through which to feed the attachment fitting at the leading edge of the belt, together with its associated cable ends, shackles, and so forth, and it is also very difficult to string the cable for pulling the belt through this space, especially a cable of the size which is necessary to support the weight of such a massive belt. Even if it is possible to fit the cable through the space, the weight and inflexibility of the cable renders it an arduous and time-consuming task to thread it through each of these spaces, being that this task is normally performed manually.
It has been proposed to overcome these problems by lowering the belt downwardly from the top of the slope. However, this has not been done successfully, again because of the weight of the belt, which can lead to uncontrolled unwinding of the belt from its reel. Accordingly, the problem arises as to how to gradually lower the belt down the slope without losing control. One attempt which was made to do this involved the use of a brake consisting of heavy steel plates positioned on top of and below the belt. Bolts extended between the plates on both sides of the belt, and these were tightened manually to provide a braking force. However, this attempt failed in practice: not only was the use of manually tightened bolts to provide the braking force too slow and cumbersome to provide acceptable reaction times, but it was found that as the bolts were tightened along the sides of the belt, the middle portions of the plates deflected so that there was relatively little braking force at the center of the belt. In fact, when this deflection and the resultant loss of braking force occurred, the natural response of the operators was to further tighten the bolts, which increased the deflection and further decreased the braking force, resulting in a runaway belt.
Another approach which has been attempted to provide controlled lowering of the belt has involved the use of two separate clamp assemblies. Each clamp assembly is provided with a strongback which extends across the belt, with bolts passing through this so that force can be applied at the center of the belt as well as at the edges. The clamps are spaced apart by about 100 feet along the belt, and a winch cable is attached to the upper one. The upper clamp is tightened, using a large ratchet wrench; the lower clamp is then loosened and the upper clamp is lowered down to it using the winch, together with the belt which is held therein. The lower clamp is then tightened to hold the belt in place, and the upper clamp is loosened and pulled back up to its upper position so that the process can be repeated. While this technique enjoys certain advantages over some of its competitors in terms of control, it is obvious that this "inchworm" process, which advances the belt only some 100 feet at a time, is very time consuming and inefficient, especially when dealing with belt runs which are several miles long. Furthermore, this process still requires the use of a massive winch which is capable of handling the weight of the belt, and the need to install this at the top of the belt run. Also, the technique requires that 100 feet of open space be available on the belt, and in many cases this simply does not exist.
As an incidental matter, while applicant is aware that the techniques described in the preceding two paragraphs have been attempted in various parts of the world, no admission is made that these constitute prior art with respect to the present invention. Rather, these approaches are described here to illustrate the ongoing and generally unsuccessful attempts which are being made to solve the problem of how to install belts on these very large conveyor belt systems.
Accordingly, there exists a need for a method and apparatus for installing belts on very large conveyor belt systems which avoid the need to pull the belt up inclines when installing it. Furthermore, there exists a need for such a method and apparatus which provides for controlled, lowering of the belt from the top of inclines or declines, and for the effective and rapidly adjustable application of braking force for doing this. Still further, there exists a need for an apparatus for providing such an effective and rapidly adjustable braking force, and which applies that braking force across the entire width of the belt, instead of applying a braking force which is concentrated at the side edges of the belt.